The Regulatory Mechanism Of Bacterial Heavy Metal And Antibiotic Resistance Mediated By Montmorillonite Upon Cadmium Stress

Cadmium?Cd?is a toxic heavy metal.Its high background value in environmental media makes it an important concerned.Chronic Cd exposure can threaten microbes and induce bacteria to develop resistance of heavy metals and antibiotics.Resistance is an effective survival mechanism for bacteria,but it may cause the spread and proliferate of antibiotic resistance genes?ARGs?,threatening the ecosystem and human health.Clay minerals,the most active components in soil,generally coexist with heavy metals and microbes in contaminated soil.There are complex interfacial interactions among them.Therefore,under heavy metals stress,clay minerals may affect resistance by regulating bacterial gene expression and play an important role in the generation and transmission of ARGs.The main contents of this article are as followed:?1?Chryseobacterium sp.WAL2,isolated from the natural soil,was exposed to a series of gradient concentrations of Cd(16,32,64 and 128?g?m L^-1)for 12 d in the presence and absence of montmorillonite?Mt?.Cd was highly enriched by the unique interface interactions between Mt and bacteria?67.6-82.1%?,leading to a more hostile environment for bacterial cells.However,Mt ultimately enhanced bacterial resistance to Cd stress by stimulating the mechanism of bacterial resistance;namely:?i?Mt increased genes expression connected with ion transport,enhancing the uptake of Cd;?ii?Mt stimulated genes expression related to efflux pump and positively regulated cellular oxidative stress?e.g.,glutathione?and Cd accumulation?e.g.,cysteine?processes.Further,genes expression related to intracellular metabolic processes was enforced,which supplied a driving force and accelerated electron transfer;?iii?Mt improved genes expression involved in DNA replication and other biological processes to maintain bacterial vitality.?2?Escherichia coli?E.coli?,a lab-mode strain,was exposed to a series of gradient concentrations of Cd(16,32,64 96 and 128?g?m L^-1)for 15 d in the presence and absence of Mt.RNA-seq results showed that Cd induced up-regulated expression of genes related to antibiotic resistant such as penicillin,tetracycline,macroliactone,chloramphenicol,multidrug efflux and multidrug resistance.Mt weakened the up-regulated expression of these genes.The results of MIC and q RT-PCR also confirmed that Cd could induce antibiotic resistance of E.coli and Mt could decrease the resistance.Further biological function analysis,a regulatory mechanism of E.coli antibiotic resistance mediated by Mt upon Cd stress was proposed:Mt could reduce antibiotic resistance by alleviating the expressions of genes involved in cell wall/membrane,protein synthesis,transport systems,signal transduction,and energy supply processes.Therefore,this study not only provided a novel insight for environmental mitigation of heavy metals from the perspective of molecular biology,but also highlighted a new theme that clay mineral could mitigate the environmental stress and ecological risks of ARGs induced by heavy metals.